Quote:
Originally Posted by renault_megane_dci
Modern Atkinson cycle engines
A small engine with Atkinson-style linkages between the piston and flywheel. Modern Atkinson cycle engines do away with this complex energy path.Recently Atkinson cycle has been used to describe a modified Otto cycle engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold. The effective compression ratio is reduced (for a time the air is escaping the cylinder freely rather than being compressed) but the expansion ratio is unchanged. This means the compression ratio is smaller than the expansion ratio. Heat gained from burning fuel increases the pressure, thereby forcing the piston to move, expanding the air volume beyond the volume when compression began. The goal of the modern Atkinson cycle is to allow the pressure in the combustion chamber at the end of the power stroke to be equal to atmospheric pressure; when this occurs, all the available energy has been obtained from the combustion process. For any given portion of air, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.
The disadvantage of the four-stroke Atkinson cycle engine versus the more common Otto cycle engine is reduced power density. Due to a smaller portion of the compression stroke being devoted to compressing the intake air, an Atkinson cycle engine does not take in as much air as would a similarly designed and sized Otto cycle engine.
Four-stroke engines of this type with this same type of intake valve motion but with a supercharger to make up for the loss of power density are known as Miller cycle engines.
( Atkinson cycle - Wikipedia, the free encyclopedia)
The compression ratio increase is one of the difficulties I raised but one more that springs to mind is the intake sizing (valves and carb) is gonna be too big on a velocity point of view.
Engine swap is very difficult in France (homologation required) |
Okay, I did some more digging and I think we just differed over semantics.
When I was referring to the Atkinson cycle, I was thinking of the "original" Atkison engine (1882) like this:
workaround ideas to discuss among friends: Atkinson cycle: a nice marketing strategy to fool the hybrid car buyers
that uses a different mechanical mechanism, rather than different valve timing.
In 1957, the so-called Miller cycle was introduced which accomplishes the same goal as the Atkinson cycle through IVC adjustment and, yes, sometimes includes a supercharger.
All production engines that I'm aware of that are called "Atkinson cycle" do not have the non-traditional mechanism, and use IVC adjustment.
So whether it's called Atkinson or Miller, we're talking about the same thing.
Sorry for the confusion.